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Investigating further I identified that there was BVD virus circulating in these animals, reducing the calves' immunity and exacerbating the pneumonia.

Bovine Viral Diarrhoea (BVD) is, as the name suggests, a virus that infects cattle, and can appear in a herd in a number of different ways, depending on the herd's immune and reproductive status. Diarrhoea, respiratory infection, infertility and abortion are the most common clinical signs of the disease when the disease is first introduced, but the endemic situation in many herds, is more significant and has often been underestimated in terms of its affects on animal health and the economics of the farm.

The long-term effects caused by a herd infection are infertility and abortion, but also weak calves and persistently infected calves (PI) that are the reservoir for infecting others on the farm.  A cow infected in the first half of pregnancy will lead to infection before the development of the calf's immune system. Thus, the calf remains infected and is a source of infection throughout its life. BVD virus has also been identified as an immunosuppressive agent, and reduces the calf's own immune system, increasing the risk of infections such as respiratory disease and scours and making them much more difficult to treat.

On analysis of your herd's fertility data, if you notice an increase in the number of irregular returns to service, if this cow is having intervals of 25-36 days between heats, then, consider BVD as a potential cause. (Bad heat detection can also cause these irregular returns!)

If BVD is suspected, then there are good diagnostic tests to identify both the PI animals and also the antibody status of the herd. If you are a dairy farmer, then a simple bulk milk tank test can look for antibodies to BVD, and can also screen for PI's, in beef, it will require bleeding a selected group,but this means we can identify if BVD is present on the farm.

If BVD virus is identified on your farm, then there are good vaccines available to protect your breeding cattle and prevent the creation and birth of more PI's. Because of this it is now possible to control BVD at farm level, and the disease could be eradicated completely from your farm.

If you have any concerns over BVD please contact your local VET

Paul Horwood BVetMed DBR MRCVS